Talking to your Sara-N2xx with only serial connector.
On request, I have cross-posted this topic:
The idea is simple, the NB-IOT module in principle requires 3.3V power and TTL - serial connection to work.. This will enable you to experiment without an Arduino shield as an intermediate...
I have included a 3.3v power regulator as the voltage on my ultra cheap e-bay USB-Serial connector was a little on the high side... Of course, if you have a 3.3 voltage source you trust then you can safely eliminate the regulator in the schematic...
Similar wiring could also be used to hook up STM32... esp modules and so on..
Note: You might wonder why I only connected 3 of the four Arduino ports ... Well the fourth connector is misaligned with a standard print / prototype board and it is not needed anyway.